One that comes to mind is ML, which was originally developed as a domain-specific language for writing proof tactics in the LCF theorem prover, and was only later broken out into a standalone programming language.
I can't think of one canonical companion project for them, but early Lisp, COBOL, and FORTRAN were also pretty driven by external application concerns, in AI, business logic, and numerical simulation, respectively.
The original McCarthy LISP started even more abstract than ML: it was intended as a logical thought exercise, and was only accidentally a programming language at all.
COBOL (and Ada) were standards-first languages. The industry-driven standards committees designed the languages first, and it was not until afterwards that there were working implementations, much less working programs. Industry experience guided them in later releases, but v1.0 (which Rust is still working towards) were even more ivory-tower than languages whose only program is their own compiler.
I can't think of one canonical companion project for them, but early Lisp, COBOL, and FORTRAN were also pretty driven by external application concerns, in AI, business logic, and numerical simulation, respectively.